Method and apparatus for determining the field strength of dynamo-electric machines.



E. C. BALLMAN. METHOD AND APPARATUS FOR-DETERMINING THE FIELD STRENGTH 0F DYNANIO ELECTRIC MACHINES.

APPLICATION FILED APR. 3. IQI-fi.

PuIQIlId June 18, 1918.

w w W a 4 W I 4 0 l H "Z M k m [OW/N C. BALL NA N) 659 iorce divided by magnets used in magnetos, lose t e1r magnetism after use, with the result that the l' voltage of the m gneto will drop so low that X the magneto; W111 not generate current of Now the electromotive force i'sa function theprop r voltage r the lgn'ltlon g of the field strength and of the speed, and g y an t q y, may, therefore, be represented by SMK, l W 13 1 g and Causes, where S .represents the speed M the field W {5W6 all "regular a l fi g VQltstrength, and K a constant. Furthermore, g l y, to the y g g pthe reactance X, being a function of the fre- Heretofole I h b dlfllcult F? test quency, is also a function of the speed, and magnetos, for the reason that, to do so, it was th f b t d b SLk, P yto the magneto t Predeter' where L represents the coeflicient of self-ini'mlnQd constant p a n Observe ductance, and k another constant. The last r d g of a Q Q and compare equation can, therefore, be written as ,folsame with-a. test reading; this, however,.re-, l y I quires the dismounting of the magneto from K MKv theautomobile, and its operation by a con- C UNITED sjTAT s PATENT OFFICE,

EDWIN C. BALLMAN, 015 LOUIS, MISSOURI,

- ,WI-IITTEN, OF ST. LOUIS, MISSOURI.

ASSIGNOR or ONE-HALF T0 STAHL A.

y nTHon AND APPARATUS r012 DETERMINING THE FIELD STRENGTH or DYNAMO- ELECTRIC MACHINES.

Application filed April 3, 1916.

To all whom z't may concern.

Be it known that I, EDWIN O. BALLMAN, a citizen of the United States, and; residing at St. Louis, in the State of Missouri, have relates to method and apparatus for determining the field strength of dynamo electric machines, and more particularly, method and apparatus for determining the strength and condition of the permanent magnets of a magneto.

As-is well known, these-called erma-nent stant'speed prime mover. It will be obvious that this is a tedious and neto 'is built into the automobile.

' machine, such as sitat1ng"the operation of such a machine at Some of- .the objects of this invention,

therefore are to provide method and, ap

paratus for determining the field strength.

and other conditionsof a dynamo electric a magneto; without .necesa predetermined constant speed, and without requiring the dismounting of such a machine from its place of installation.

' Further" objects will appear from the ,de-

tail description taken in connection wi th; the

Figure 1 1s a lan view of an apparatus embodying this invention, the cover being removed so as to showthe interior pa rts:

Specification of Letters Patent.

costly operation, more especially in machlnes where the-magpart of the total reluctance,

rent insuch a circuit. will vary Serial No. 88,693. 1

If the resistance R is small as compared to the reactance X, then the current will ractically be' equal to the. electroinotive the reactance, or:

Now the coefiicient of self-induction L isa function of the permeability of the magnet1c circuit. Where the magnetic circuit is wholly a ferric circuit, the permeab1l1ty,i t'nd thereof, L, of course,

varies with the speed. If, however,

the magnetic circuit is made up of ferric and non-ferricparts, and if the re,

luctance of the non-ferric partis a large then L will be practically constant for 'all speeds, or at least for allspeeds over a considerable Considering, therefore, that L is a constant, we can rewriteothe lastequation as follows:

a constant, the ouronly. w th the Since the fraction is Patented June 18,1918;

on the line 2 2, Fig. l; i

range.

' field strength, and the measure of the cur- Connected in circuit with the magneto 1s a standard field magnet and measuring means,

a measure of the field rent is, therefore, 1 d f h tie Spec 0 t e 6 which moves over a suitable scale 7 Connected in series with the field coil 4 is a reactance coil 8, the lroncore 9 of which has an air gap, as shown. The terminals of the been shown,

instrument are indicated at 10. 7 I

In accordance with this invention, a field coil 4 ofvery low resistance is used, and the reactance coil 8 is also made of low resist ance, so that the resistance of the circuit of the instrument will be very small'compared with the reactance. The reactance'deviceis also so proportioned that the non-ferric part of the magnetic circuit, or the air gap, will represent about ninety-five percent. (95%) of the total reluctance. YVith an instrument designed as specified, the current traversing the circuit will be independent of the fre-- quency, and, therefore, of. the speed at which the magneto is run, and this current will, therefore,vary directly and solely with and will be a direct and sole function of the field strength of the machine. The instrument, when connected across the terminals of a magneto, the strength of the magneto field.

In Figs. 1, 2 and 3 is shown 'a practical device embodying this invention, lar parts have been indicated by. the-same reference characters as in Fig. 4. The field coil 4 of the current. measuring means is wound on abrass spool 11, and the vane 5 is mounted on a pivot 12, which also carries the pointer 6 moving over the scale 7 attached to the spool. The pivot 12is connected toone end of a spiral spring 13, the

other end of which is connected'to an arm 14 adj'ustably mounted ona bracket 16 on the spool.' Passing through the spool is a soft iron bar or pin 15, which acts to repel the vane35, and an adjusting device 17 in the form of-a plate ofsoft iron, is mounted on the spool and adjustable about its pivoted end, so as to adjust the instrument. current measuring means may of course be of any suitable construction.-

Connected in series with the'coil 4, and

across the binding post 10, is the reactance coil 8, which is mounted on a laminated core 9, preferably of H-form, the coil so wound .strument, therefore,

will, vtherefore, indicate directly and,simispeed, and

The

being mounted in a soft iron cylinder 90, the core being'positioned in the cylinder by means of ebonite pins roper air gap; The reactance, as well as the current measuring means, is. firmly mounted in a case-19, which has a glass cover 20. The scale 7 may be provided with any suitable graduations.

lVhen the binding posts 10 are connected across the terminals of a magneto, andthe magneto is run at a moderate speed, the pointer 6 will be positioned on' the scale to a position depending upon the "field strength of the magneto. By providing a table giving the proper field strengths of different makes of magnetos, rectly on'the scale, the instrument will indicate at :aglance whether the field strength has decreased sufficiently to require re-1nagnetization of the magnets.

Since, as as the reading of the instrument 18, so as to obtain theis independent of the speed, the magneto can be tested directly on the automobile bysimply running the engine and the magneto at a moderate speed. Since the instrument indicates dlrectly the field strength of the magneto, variations and fluctuations in this strength due to irregular air gap, bad bear-- ings, etc., are directly indicated. This infurnishes a convenient inlians for readily. testing magnetos andthe 1 e- I 1 I It is obvious that various changes maybe made in the details of the method and apparatus Without departing from the spiritof this invention, audit. is, therefore, to be understood that this invention is not to be limited to the specific shown.

Having thus described the invention, what is claimed is z 1. The method of" determining the field strength of a dynamo-electric machine, com-- prising maintaining the value of the current delivered by the machine independent of its measuring the current delivered.

details described and 2. The method of determining the field strength of a dynamo-electric machine, comprising maintaining the value of the current delivered by the machine as a direct and sole function of the field strength, and measuring the current delivered. I

' 3. The method of determining the field strengthpf a dynamo-electric machine, comprising varying the impedance of the circuit of the machine directly and solely in accordance with its speed, and measuring the current delivered by the machine.

4. The method of determining the field strength of a dynamo-electric machine, comprising connecting, in chine a reactance whose value is a direct and sole function of the speed, and measuring the current inthe circuit.

,5. The method of determining circuit with the .ma-

the field prising connecting in circuit with the mastrength chine a reactance Whose magnetic reluctance is. substantially constant, and measuring the current in the circuit.

-6. An apparatus for determining the field strength of dynamo-electric machines, comprising current measuring means adapted forconnection in circuit with a dynamoeleetric machine, and means for maintaining the value of the current as a direct and sole function .of the field strength of the ma- .chine.

- 7. An apparatus for determining the field of dynamo-electric machines, comprising current measuring means adapted for connection in circuit With a dynamo-ele'c tric machine, and means for maintaining the value of the current independent of the speed of'the machine.

8. .An-apparatus for determining the field strength of' dynamo-electric machines, comprising current measuring means adapted for, connection in circuit with a dynamo-electric machine, and means for varying the impedan'ce of said circuit in accordance with the speed of the machine.

9. An apparatus for determining the field strength of dynamo-electric machines, com-- prising current measurin means, and means for maintaining the va ue of the current traversing said measuring means inde pendent of its frequency.

10'. An apparatus for determining the field strengthof dynamo-electric machines,

comprising current measuring means, and means for varyingthe impedance of the current measuring means circuit in accordance with the frequency of the current traversing said circuit.

11. An apparatus for determining the field strength of dynamo-electric machines, comprising current measuring means, and a re actance in circuit with said measuring means adapted to maintain the value of the current traversing said measuring means independent of its frequency.

12. An apparatus for determining the field strength of dynamo-electric machines, comprising current measuring means, and a reactance in circuit with said measuring means, said reactance being constructed so that its coefficient of reactanee is substantially constant.

13. An apparatus for determining the field strength of dynamo-electric machines,

comprising current measuring means, and

a reactancc in circuit with said measuring means, said rcactance having a magnetic circuit whose reluctance remains substantially constant. I

14. An apparatus for field strength of dynamo-electric machines, comprising current measuring means, and a reactance in circuit with said measuring means, said reactance having a combination ferric and non-ferric magnetic circuit, the reluctance of the ferric part being relatively small with respect to the reluctance of the non-ferric part.

15. An apparatus for determining the field strength of dynamo-electric machines, comprising current measuring means, and a reactance in circuit with said measuring means, said reactance being constructed so that its coefficient of reactance is substantially constant, the resistance of said circuit being small compared to the reactance thereof.

In testimony whereof I aflix my signature this 11th day of February, 1916.

EDWIN C. BALLMAN.

determining the 

